Loud-speaker



June 1-0, 1930" M. c. HOYPKI!I\IIS 3,95

. LOUD SPEA ER inal Filed March'25, 1926 3 SheetsSh eet -l iNVENTQ mAagus c. HOP 5 v ATTORNEYS- Jun 10, 1930;

. k M. c. HOPKINS LOUD SPEAKER Original Filed March 23, 1926 3 Sheets-Sheet 2 INVENTOR MARCUS C.HOPK|NS I ATTORNEYS June 10,1930; M. CHOPKINS 1,763,052

L-OUD SPEAKER ori inal Filed-March 25, 1926 5 Shee tS-Sheet s INVENTOR. I MARCUS QHOPKINS 'AT TORNEY5 1 Patented June 1.0, 1930 PATENT OFFICE MARCUS C. HOPKINS, OF WASHINGTON, DISTRICT OF COLUMBIA, ASSIGNOR TO HOP- KINS CORPORATION, OF JERSEY CITY,

WARE

NEW JERSEY, A CORPORATION OF DEM-- LOUD-SPEAKER Application filed March 23, 1926, Serial No. 96,743. Renewed April 22, 1930.

The present invention relates to loud speakers of the type disclosed in my copending application, Serial No. 77033, filed December 22, 1925. The loud speaker disclosed in that application comprises a central relatively light and stiff diaphragm or tympanum, preferably conical in shape, and a surrounding external sound board or resonator having greater mass than that of the central diaphragm. The connection between the central diaphragm and the external resonator or sound board is such that the central diaphragm will respond to the relatively high frequencies and will efliciently reproduce the high tones or sounds, and the relatively low frequencies will be transmitted through said connection to the sound board so that it will respond to the relatively low frequencies and will elliciently reproduce them.

The sound board or resonator can conveniently be made of three ply veneer with the grain of the inner ply running transverse to the grain of the two outer plies. Fir and spruce may be used for this gurp'ose with good results. Also the sound card can be made of balsa wood as described and claimed in my copending application, Serial No. 79,329, filed January 5, 1926. Preferably, however, the sound board is made of synthetic lumber, and by this'term I intend to include relatively rigid sheets or boards made from fibers that have been separated, in part, at least, and then reassembled in heterogeneous arrangement in anew assembly, as described and claimed in my copending application, Serial No. 87,491, filed February 11, 1926.

The present invention is directed particularly toward reinforcing the edge of the sound board to protect the board during shipment and use and to improve its appearance, but particularly to control any warping or any tendency toward deformation due to changes in atmospheric conditions, or resultin from aging of the board.

Vhile in use the board may vibrate violently, particularly at its outer edge, and conse uently, care must be taken notto have anything attached to that edge that could become loosened and rattle. Also, from a phonetic standpoint, the weight of the edge bears a rather import-ant relation to the weight and size of the sound board, and to the diameter, weight and size of the cone, and to the distance through which the apex of the cone is moved by the electrical movement, and with what power it is moved.

Having in mind all of the foregoing factors, I have devised a reinforcement-or binding for the edge of the sound board whereby physical support is given to the board in ad- "antageous manner and its sound producing qualities are not impaired and under some conditions are improved. Fig. 1 is a front view of a loud speaker especially designed for use in hotels, theatres, concert halls and similar places where a large volume of sound is desired;

Fig. 2 is a side elevation of the speaker shown in Fig. 1;

Fig. 3 is a rear view of theloud speaker shown in Fig. 1;

Fig. 4 is a vertical section taken 011 the line 4-4 of Fig. 3; Fig. 5 is an enlarged detail vertical section of the central portion of the loud speaker showing the connection between the central diaphragm and the external sound board or resonator;

Fig. 6 is a front elevation of another type of loud speaker operating on the same principal as that shown in Fig. 1;

Fig. 7 is a top plan view of the loud speaker shown in Fig. 6;

Fig. 8 is a rear elevation of the speaker shown in Fig. 6;

Fig. 9 is a vertical section taken on the line 9-9 of Fig. 8;

Fig. 10 is a perspective view of the lowermost section of the reinforcing molding.

Referring first to Figs. 1 to 5 inclusive, the loud speaker shown in these figures comprises a central conical diaphragm or tympanum 1 coupled to a vibratory resonator or sound board 2 by means of a semifiexible coupling, shown in Fig. The conical diaphragm 1. is preferably made of paper, cut and folded to shape and glued along a radial seam. Near the outer edge of the cone thus formed, the paper is creased and then folded .up to form a forwardly flaring brim 3 (Fig.

5). This brim naturally assumes an angle to the plane of the base equal to the angle between the radial elements of the cone and that base. The outer edge portion of the brim 3 is preferably glued to the inner circular edge of the resonator or sound board 2. For this purpose the inner circular edge of the sound board is tapered as shown at 4 and the outer edge portion of the brim 3 seats upon and is glued to the tapering surface thus formed. In gluing or cementing the brim to the beveled edge at it is important that a partof the brim be left free to form a hinge on which the cone may float. Thus with a brim A wide the cemented portion may have a width of A, more or less and the remainder of the brim may be left free to swing.

The resonator or sound board Qshown in the drawing is octagonal in shape and is made of synthetic lumber.

The vibratory actuating force is applied to the apex of the conical diaphragm by means of a rod or wire 5 which is adapted to be maintained in fixed relation with the diaphragm by means of a set screw 6. The rod 5 maybe actuated by electromagnetic mechanism housed in the casing 7. The casing 7 may be attached to a support or spider 8 which in turn may be afiixed to the resonator or sound board by means of wood screws 9.

While the loud speaker shown in Figs. 1

\ to 5 inclusive may be made of any desired size.

within reasonable limits, it has been found that for concert work excellent results have been obtained by making the conical diaphragm approximately 17 inches in outside diameter and the resonator or sound board approximately 4 feet in outside diameter. The relatively large size of the loud speaker shown in Figs. 1 to 5 inclusive makes it desirable to suspend it in any suitable way instead of supporting it from below.

The reinforcement at the edge of the loud speaker comprises a plurality of wood sections 10 each in the form of a double molding as shown in Fig. 5, and made in continuous lengths by suitably grooving a wood strip. Each section 10 is cut to the proper length with its ends beveled, and then its trough or groove is coated with glue. The section is then slipped on over the edge of the sound board with which it makes a tightfit and to which it becomes firmly attached by setting of the glue. Although nails may be used to supplement the glued connection, I find it inadvisable to use them because of their tendency to work loose and rattle. I also find it best not to glue or nail one wood section to-the adjoining sections. Any sound board of this general character has a tendency to warp with age, and also may contract or expand slightly with changes in the moisture content of the surrounding atmosphere. The edge reinforcement above described restrains warping of the board as a whole, but it gives enough freedom at the edge to permitthe board to expand or contract slightly without setting up detrimental stresses in the board which might impair its sound producing action.

The loud speaker shown in Figs. 6 to 9, inclusive, is very similar in construction to that above described. It comprises a conical tympanum 1, a sounding board or resonator 2, a spider 8 for supporting the casing 7' of the electromagnetic actuating mechanism, and a forwardly flaring brim 3 on the cone which is attached to the inner edge of the sound board in the same manner as explained in connection with Figs. 1 to 5. The resonator or sound board 2 of this form of loud speaker is alsomade of synthetic lumber as in the case of the loud speaker described above. The main difference between the speaker shown in Figs. 6 to 9, inclusive, and that shown in the first five figures is that the sound board or resonator 2 is of smaller diameter. The conical diaphragm 1' may or -may not be smaller than the conical diaphragm of the loud speaker of Figures 1 to 5. he reduction -in overall size of the loud speaker shown in Figures 6 to 9, inclusive makes it possible to support the speaker on a table or other horizontal surface and for this reason the sound board 2" is provided with suitable legs orcross pieces 11, preferably made integral with the lowermost section 10 as best shown in Fig. 10. In constructing a loud speaker of the type shown in Figs. 6 to 9, I have found that excellent results are obtained by making the cone 2 approxi mately 15 in diameter and the sound board approximately 22" in diameter. This makes the transverse width of the annular sound board approximately 3 but good results may be obtained by making the sound board of even less width than this or of even greater width than the sound board shown in Figs. 1 to 5 inclusive.

In both types of speaker the central conical diaphragm efficiently reproduces the higher tones and perhaps some of the intermediate tones while the surrounding annular resonator or sound board efficiently reproduces the lower or bass notes. These relatively large sound boards, particularly if made of synthetic lumber, gives a very true and faithful reproduction of the lower or bass notes, and reinforcing the edge of. the board with wood, as above described, appears to have the effect of saving basic qualities that otherwise might be lost. The lower notes are not only accurately reproduced, but the tonal quality is excellent, the reproduction being soft and mellow.

In a loud speaker constructed in accordance with the foregoing description, the regenerated or reproduced sound waves are substantially directly proportional both quantitatively and qualitatively to the actuating force and the sound so reproduced retains substantially the same balance of high and low tones as the original sound from which the actuating force was derived.

One suitable material is made from bagasse and other fibrous material by separating the I fibres of the raw material and then reassembling them in a felted, heterogeneous arrangement either with or without the addi- Another suitable material is made fromv wood by physically separating the fibres and then, after physical or other treatment, .reassembling them in heterogeneous felted arrangementof a relatively r1 'd nature and of a porous texture as describe in United States Letters Patent Nds. 1,631,171, 1,631,172 and 1,631,173. j 3

- Still another material is made from paper mill screenin s, reassembled as described at length in nited States Patents Nos. 1,153,512 and 1,187,476.

These three materials are typicalof that class of materials which-I have chosen to call synthetic lumber. Insulite is the best for general use, but very brilliant results may a had from using the material of Patent Nos. 1,631,171, 1,631,172 and 1,631,173. The results with the first. mentioned material are acceptable, but the material seems to lack either a stiffness in the individual fibres or a lack of secure attachment between one fibre and its fellows where they cross one another in their heterogeneous arrangement. Individually the fibres should be stifi', and collectively they-should rigidly interlock to form a porous rigid mass. Just why that is, I do not know. 1

I claim:

1. A loud speaker having a sound board with a polygonal periphery, and a strip of protecting and reinforcin molding secured to the sound board along tl ie' peripheral edge of each side of the olygon.

2. A loud speaker comprising a central relatively light and stiff diaphragm, an external soundboard of reater mass than the diaphragm, and a flexi le coupling between the two having such flexibility that the entral diaphragm will respond to relatively high frequencies and having such rigidity as to transmit the relatively low frequencies to the sound board, said sound board having a peripherally dis osed reinforcement.

3. A loud spea er comprising a central conical diaphragm made of fibrous material, an external annular flat sound board, and aflextect the edge of the sound board.

ible coupling between 'said diaphragm and the sound board having such flexibility that the conical diaphragm will respond to relatively high frequencies and having such rigidity as to transmit the relatively low frequencies to the sound board and said sound board having a peripherally disposed reinforcement.

4. In a loud speakerthe combination of a fibrous vibratory cone, a thin wood resonator operatively connected to the periphery of said cone, and a wood rim secured to and stifiening the edge of said resonator, substantially as described.

'5. In a loud speaker the combination of a fibrousvibratory cone having a forwardly bent brim, a thin annular resonator provided with a beveled-inner edge to which said brim is secured, and a wood -riin secured to and stiffening the edge of said resonator.

6. A loud speaker having a flat sound board at least the major edge portion of which is unrestrained and free to vibrate, and a strip of molding made of sti'fl' material secured to the sound board entirely around its edge portion, the molding at the unrestrained edge portion of the sound board being attached only to the sound board and being vibratable therewith and serving to reinforce and pro- 7. A loud speaker having a flat sound board at least the major edge portion of which is unrestrained and free to vibrate, and a stiff wooden moldingapplied entirely around the edge portion of the sound board, the molding at the unrestrained edge portion of the sound board being attached only to the sound board and being vibratable therewith and serving to reinforce and protect the edge of the sound board.

8. A loud speaker having a wooden sound boardat least the major edge portionof which is unrestrained and free to vibrate, and a channeled molding applied entirely around the peripheral edge of the sound board, the

,edge portion of the sound board being held in the channel of the molding and the mold-' ing at the unrestrained-edge portion of the sound. board being attached only to the sound board and being vibratable therewith.

9. A loud speaker having a soundboard made of synthetic lumber at least the major edge portion of which is unrestrained and free to vibrate, and a channeled molding applied entirely around the peripheral edge of edge of each side of the polygon, said reinforcing and protecting strips being independent of each other, and supporting means for the speaker associated with the lowermost reinforcing strip.

In testimony whereof I afiix my signature.

MARCUS C. HOPKINS. 

